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BUREAU OF MINES ^?.^ 
INFORMATION CIRCULAR/1989 



Framework for Autonomous Navigation 
of a Continuous IVIining iVIachine: 
Face Navigation 



By Donna L. Anderson 



UNITED STATES DEPARTMENT OF THE INTERIOR 



Information Circular 9214 



Framework for Autonomous Navigation 
of a Continuous IVIining IVIachine: 
Face Navigation 

By Donna L. Anderson 



UNITED STATES DEPARTMENT OF THE INTERIOR 
Manuel J. Lujan, Jr., Secretary 

BUREAU OF MINES 
T S Ary, Director 







Library of Congress Cataloging in Publication Data: 



Anderson, Donna L. 

Framework for autonomous navigation of a continuous mining machine: face 
navigation. 

(Bureau of Mines information circular; 9214) 

Includes bibliographical references. 

Supt. of Docs, no.: I 28.27:9214. 

1. Coal-mining machinery. 2. Vehicles, Remotely piloted. I. Title. II. Series: 
Information circular (United States. Bureau of Mines); 9214. 



^^295,114 



[TN813] 



622 s [622'.334] 



88-600437 



CONTENTS 

Page 

Abstract 1 

Introduction 2 

Information and control requirements 2 

Tasks of autonomous navigation in mines 2 

Navigational tasks of continuous mining machine 2 

Face navigation of continuous mining machine 2 

Ahgnment at face 3 

Guidance during cutting sequence 4 

Local navigation of continuous mining machine 4 

Traunming through entry 4 

Turning corner 4 

Global navigation of continuous mining machine 4 

Generate path 4 

FoUow path 4 

Update map 6 

Previous research and attempts in remote and autonomous navigation of continuous mining machines .... 6 

Laser alignment sensor for continuous mining machines 6 

Assessment of optic guidance and supervisory methods 6 

Preliminary design of automated continuous mining machine with remote override 7 

Conclusions of research 7 

Face navigation 7 

Reference for desired cut 8 

Guidance during cutting sequence 8 

Local navigation 8 

Find path 8 

Follow path 9 

Global navigation 9 

Generate path 9 

Follow path 9 

Summary 9 

Sensory system, data manipulation, and control programming 10 

Introduction 10 

Autonomous face navigation of continuous mining machine 10 

Reference for desired cut 10 

Description of guidance from MCS 11 

Benefits of guidance from MCS 11 

Disadvantages of MCS reference system 12 

Navigational guidance system 12 

Sensory solution 12 

Determining position and heading using laser-based scanning system 13 

Determining lateral position and heading using ultrasonic ranging units 16 

Monitoring system 16 

Integration system 17 

Navigational goal scheduler 17 

Action planner 18 

Navigational test-beds 18 

Conclusions 20 

Appendix.-Research issues in autonomous navigation 21 



ILLUSTRATIONS 



Page 



1. Typical room-and-pillar mining section 3 

2. Maneuvering for straight-cut 5 

3. Maneuvering sequence for crosscut 5 

4. Mobile roof support 10 

5. Continuous miner advancing face under MCS 11 

6. Block diagram of the hardware-software systems and information transfer for proposed navigational 

guidance system 13 

7. Method 1 for determining position and heading of continuous miner relative to MCS 14 

8. Mathematical representation of method 1 for position determination 14 

9. Method 2 for determining position and heading of continuous miner relative to MCS 15 

10. Mathematical representation of method 2 for position determination 15 

11. Joy 16CM available continuous mining machine 19 





UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 


7h 


degree per hour 


h 


hour 


Vmin degree per minute 


in 


inch 


ft 


foot 


^ min 


minute 



I 



FRAMEWORK FOR AUTONOMOUS NAVIGATION 

OF A CONTINUOUS MINING MACHINE: 

FACE NAVIGATION 

By Donna L. Anderson^ 



ABSTRACT 

The first section of this U.S. Bureau of Mines report includes a discussion of the navigational tasks 
performed by operators of mobile mining equipment, with the focus on the navigational information and 
guidance techniques required by continuous mining machine operators. Some previous research and 
attempts in remote £md autonomous navigation of continuous mining machines are mentioned. Issues 
of research in autonomous navigation of various other mobile robots are presented, with attention 
focused on their applicability to a continuous mining machine navigating in the mining environment. 
Conclusions are stated on methods of automating the navigational tasks of a continuous mining machine, 
and a decision to concentrate initial attempts on the tasks of autonomous face navigation is defended. 

The second section of this report includes a presentation of the Bureau's proposed solution for 
autonomous face navigation of a continuous mining machine, which includes the employment of a mobile 
roof support as a reference for guidance in the face area, and a navigational guidance system for the 
continuous mining machine. 



^Electrical engineer, Pittsburgh Research Center, U.S. Bureau of Mines, Pittsburgh, PA. 



INTRODUCTION 



This report documents the current status of the Bureau 
of Mines' research into autonomous navigation in mines. 
The purpose of this research is to support the Bureau's 
development of autonomous mining operations, which will 
result in an increase in the overall safety and productivity 
of current mining operations. Automation will permit the 
relocation of the mine worker to less hazardous areas and 
duties in a mine. 

Autonomous navigation is a significant task in the 
automation of mining processes owing to the need for 
constant relocation of mine equipment in various work 
areas of mines. Automatically controlled mobile mining 
equipment has the responsibility of navigating safely cind 



accurately throughout the immediate work area and be- 
tween work areas as if a human operator were present. 

To accomplish safe aind accurate navigation in a mine, 
the equipment must have a knowledge of the area to be 
traveled along with the capabiUties of determining a path 
in that area £ind controlling its movement along the path. 
A knowledge of the area is available via a model of the 
mine plan, which can be preprogrammed in memory, and 
a model of the immediate area, which can be obtained 
from sensory input. Intelligent software can analyze these 
models and determine traversable paths in these areas. 
Additional sensory input can be collected to monitor and 
control the mine equipment's movement along its path. 



INFORMATION AND CONTROL REQUIREMENTS 



TASKS OF AUTONOMOUS NAVIGATION IN MINES 

The navigational tasks in mines can be classified into 
three types: face, local, and global. These tasks are 
determined by observing some of the navigational duties 
necessary for each type. 

The job of face navigation is the positioning of mobile 
mining equipment in the working face area. Before the 
cutting process begins, the continuous mining machine is 
positioned at the face in the proper alignment. A shuttle 
car is positioned under the conveyor boom of the continu- 
ous miner to receive the coal cut from the face. During 
the execution of the cutting process, the continuous miner 
is guided through a sequence of operations and positions, 
which lead it to cut the appropriate area as designated by 
the mine plan. The shuttle car advances as the continuous 
miner advances and remains under the conveyor boom, 
continuing to receive coal until it is fully loaded. When 
loaded, the shuttle car leaves the face area to empty its 
load, and is replaced by a second and third empty shuttle 
car, which is positioned under the conveyor boom to re- 
ceive more coal. When the cutting process is complete, 
i.e., when the face has been advanced to the point where 
the operator is under the last row of roof bolts, the con- 
tinuous mining machine and the shuttle car leaves the face 
area to allow the roof bolting machine access to the newly 
cut area. The roof bolter is positioned under the unbolted 
roof, driUing holes and inserting bolts at the required 
spacing. 

The job of locail navigation is the guidance of mobile 
mining equipment in the local (immediate) area, excluding 
the face area, i.e., guidance around corners, through en- 
tries, and around obstacles. For example, a continuous 
mining machine is constantly maneuvering among face 
areas and is guided through various connecting passages. 
A loaded shuttle car is guided through each entry as it 
travels a predetermined path from the face to the dump 
point. 



The job of global navigation is the navigation of mobile 
mining equipment between various points in the mine, i.e., 
path planning and following from one work area to 
another. An operator of a mine haulage vehicle, e.g., must 
plan and follow a path from the material loading point to 
various work areas currently requiring the materials. 

NAVIGATIONAL TASKS OF CONTINUOUS 
MINING MACHINE 

The focus of the Bureau's research into autonomous 
navigation in mines is the navigational tasks of the contin- 
uous mining machine. An operator of a continuous miner 
performs all three different types of navigational tasks in 
mines; face, local, and global. Face navigation, although 
specific to the equipment and the task being performed, 
requires the most accuracy and reliabihty for a continuous 
mining machine. Local and global navigational tasks are 
similarly performed by operators of all mobile mining 
equipment. Therefore, any navigational techniques proven 
to work for the continuous mining machine can be applied 
to other mobile mining machinery. 

Face Navigation of Continuous Mining Machine 

An operator's objective during face navigation is to con- 
trol the position and heading of the continuous miner dur- 
ing the cutting process in order that coal is removed 
according to the mine plan. Although many different coal 
removal processes exist, i.e., full-face mining, longwall 
mining, shortwall mining, etc., this research will highlight 
the guidance for a two-pass continuous mining machine 
performing straight-cuts and crosscuts in room-and-pillar 
mining. Room-and-pillar mining is a widely used type of 
mining. A typical section is shown in figure 1. Longwall 
mining has become more prevalent in recent years; how- 
ever, room-and-pillar mining is still used for development 
of both longwall and shortwall sections. Additionally, the 



4 




Figure 1.— Typical room-and-pillar mining section. 



navigation of a two-pass machine, as opposed to a full-face 
miner, longwcdl machine, etc., includes much more maneu- 
vering and guidance. Therefore, many of the navigational 
issues will be easily applicable to other types of mining 
processes. 

The two most significant issues of face navigation are 
the alignment of the continuous mining machine at the 
face, and the guidance of the machine during the cutting 
process. The following discussion of the methods used by 
continuous miner operators to perform these tasks indi- 
cates the navigationail information and guidance techniques 
required at the face. 

Alignment at Face 

The first task of a continuous miner operator is plac- 
ing the mining machine in the correct position and heading 
at the face to begin the cutting process. The operator 



requires an indication of the position, heading, and dimen- 
sions of the desired cut. The position and heading of the 
cut is precisely mapped on a mine plan. Surveying marks, 
a laser spot, or a vertical laser guideline are located in the 
mine according to the plan, indicating the centerline of the 
entry. The continuous miner operator observes the loca- 
tion of the centerline indication to judge the correct posi- 
tion and heading for the machine at the face. 

The operator trams the machine up to the face while 
avoiding collisions with the ribs, roof, or obstacles. The 
operator is aware of the position of all exterior points of 
the machine relative to any of these objects. The brattice 
cloth is the assumed method of ventilation control, and is 
also an obstacle at the face which must be avoided by the 
continuous miner. Therefore, the operator aligns the con- 
tinuous miner at a slight angle relative to the heading of 
the desired cut. 



Guidance During Cutting Sequence 

During the execution of the cutting process, the 
operator continues to observe the location of the surveying 
marks, laser guideline, and/or the orientation of the ribs, 
and judges the position of the machine relative to the 
intended centerline of the cut. However, these actions are 
not a precise method of guiding the continuous mining 
machine, hence the accuracy of the cut is dependent on the 
operator's skill and experience. 

The maneuvering sequences for a straight cut and a 
crosscut are shown in figures 2 and 3. The continuous 
miner operator makes each cut to the appropriate height, 
width, and depth, with the centerline of the cut being as 
close to the centerline indication as possible. In practice, 
the dimensions of the desired cut are determined from the 
characteristics of the surrounding strata. However, for this 
research, a cut is assumed to be a 20-ft wide by 20-ft deep 
advancement of the face while remaining within the coal 
seam. 

The ability of the continuous mining machine to follow 
the vertical undulations of the coal seam is not within the 
scope of this project. Another current research effort at 
the Bureau is investigating coal interface detecting sensors 
for vertical guidance of coal extraction machines. The 
horizontal alignment and guidance of the continuous min- 
ing machine are the only tasks of face navigation presently 
within the scope of the Bureau's autonomous navigation 
research program. 

Local Navigation of Continuous Mining Machine 

The navigational tasks of a continuous mining machine 
in the local area consists of the guidance of the continuous 
miner through entries and around corners, while avoiding 
collisions with ribs, workers, equipment, or other obstacles. 
The following discussion of the methods used by continu- 
ous miner operators to perform these tasks indicates the 
navigational information and guidance techniques required 
for autonomous navigation in the local area of a mine. 

Tramming Through Entry 

Before tramming through an entry, an operator ob- 
serves the area in the direction of travel to find a travers- 
able path. If a path is located, and it is certain that the 
inclination is not too great and the terrain not too rough, 
the operator guides the continuous miner along the path. 

While traveling along the path, the operator is con- 
stantly aware of the position of all exterior points of the 
machine relative to the roof, ribs, and obstacles. The 
operator also watches in the direction of travel of the 
mining machine. People, supplies, trailing cables, equip- 
ment, or other mobile vehicles are common obstacles in a 
mine which must be avoided. Even small obstacles, such 
as small rocks, can hinder the navigation or even damage 
the large mining machine if encountered. To lessen navi- 
gational difficulties caused by small rocks, the operator 



may lower the gathering head, and clean the path while 
tramming. 

Turning Corner 

Corner navigation in mines is a tricky maneuver owing 
to the limited mobility of the large continuous miner in 
narrow entries. The position of the corner is observed, 
and the operator elects a proper point at which to initiate 
the turn. The operator performs a series of forward and 
backward maneuvers to execute the turn in the limited 
space. While maneuvering, the operator judges the track 
slippage to faciUtate control of the turn and turning radius 
of the machine. 

Limited visibility is another difficulty in corner navi- 
gation. An operator makes certain that people or other 
mobile vehicle operators are aware of the machine, and 
that the operator is aware of their presence, to avoid in- 
juries or collisions. 

Global Navigation of Continuous Mining Machine 

The navigation of the continuous mining machine in the 
global area consists of planning and following a path 
among work areas in the mine. This navigation requires 
the abiHty, given a map of the mine, to generate a path to 
a predetermined destination, follow that path until the des- 
tination is reached, and update the map of the mine when 
necessary. The following discussion of the methods used 
by continuous miner operators to perform these tasks indi- 
cates the navigational information and guidance techniques 
necessary for autonomous navigation in the global area of 
a mine. 

Generate Path 

Given a destination, a continuous miner operator gener- 
ates a path. The operator also determines an alternate 
path when an entry through which the operator intended 
to travel is not traversable or blocked. 

To generate paths, the operator has a knowledge of the 
common paths of travel in the particular mine. In addi- 
tion, the operator may know what areas are dangerous, 
and entries that have a difficult terrain for travel. This 
knowledge could be provided to the operator in the form 
of visual markers placed for guidance, a memory of past 
experience of the paths, or a map of the mine. 

Follow Path 

The operator travels along the route, one entry at a 
time. The operator navigates through entries until where 
to turn is recognizable. If the operator is unfamiliar v^ith 
the route, the operator may keep track of the position 
relative to the map by counting crosscuts, observing mark- 
ers on the map or in the entry, or by keeping track of dis- 
tance traveled and turns made. 




I'iim fr^ii lin iiiiiiiaiiiittiiirii liiiiriffiiiii iti 



:: 





t 



Figure 2.— Maneuvering sequence for straight-cut in room- 
and-pillar mining with a brattice cloth in the face area. 



Figure 3.— IVIaneuvering sequence for crosscut in room-and- 
pillar mining with a brattice cloth in the face area. 



Update Map 

The operator records any permanently blocked passage- 
ways on the map of the mine (or by memory), so they will 
be avoided in futm-e travel. New entries that are cut by 
the continuous miner during face navigation are likewise 
recorded, to be used as new paths of global travel, or 
indicators of globsJ position. 

PREVIOUS RESEARCH AND ATTEMPTS IN REMOTE 

AND AUTONOMOUS NAVIGATION OF 

CONTINUOUS MINING MACHINES 

Previous research into remote and automatic guidance 
of continuous mining machines provides valuable infor- 
mation to the current effort in autonomous navigation in 
mines. The following summary of research attempts is not 
complete, but gives some of the previous research that 
significantly affected the direction of the current autono- 
mous navigation project. 

Laser Alignment Sensor for Continuous 
Mining Machines 

An entry alignment sensor to provide lateral guidcmce 
for a continuous mining machine was developed and tested 
in an operating mine by Bendix under a Bureau contract.^ 
The purpose of the sensor is to provide a guideline for 
entry heading during remote or automatic control of the 
cutting process. It consists of a scanning laser source to 
project a vertical guideline, and a sensor unit containing an 
array of photodetectors to analyze the heading and lateral 
displacement of the received beam. 

The laser source, located in the entry, projects a beam 
parallel to the centerline of the desired cut. The sensor 
imit, located on the continuous mining machine, contains 
seven fresnel lenses that focus the laser guideline onto 
split photodetectors. The signals from the detectors are 
balanced when the machine is correctly positioned parallel 
to the laser guideline. An unbalanced signal is propor- 
tional to the heading displacement of the machine. Since 
an array of these split detectors are employed, the latercd 
displacement relative to the centerline is also determined. 
This information of heading and lateral displacement is 
then indicated on a display outby the machine, and used in 
remote guidance of the continuous mining machine. 

The employment of the laser source and sensor unit 
system proved to be a moderately successful means of 
remotely guiding a continuous mining machine in the 
mining environment. Some difficulties would have to be 
overcome if the system were employed for autonomous 
guidance of a continuous miner. 



Bowser, M. L. Laser Alinement Sensor for Continuous-Mining 
Machines. BuMines RI 8134, 1976, 10 pp. 



The major difficulty occurred when the beam was 
broken by obstacles. If the becun was not received by the 
sensor unit, the most recent reading was assumed until the 
beam was received again. Obviously, the reliability of the 
system was reduced, and if the beam was interrupted for 
a long period of time, the operation of the machine had to 
be suspended until the beam was received. 

Shuttle cars were the most frequent cause of beam in- 
terference. At other times, the line curtain interfered with 
the beam, and had to be moved or opened. And finally, 
undulations in the coal secun over a great distance were a 
cause of the loss of the line-of-sight. 

In summary, the Iciser alignment sensor system could 
become a successful means of autonomous guidance, if the 
laser were mounted in a position where the line-of-sight 
could be maintained. Also, the ability of the laser to ad- 
vance autonomously in the entry as the continuous mining 
machine advances would eliminate the problem of undula- 
tions in the seam causing a loss of the line-of-sight. 

Assessment of Optic Guidance 
and Supervisory Methods 

An evaluation of optical guidance systems for auto- 
mated face navigation was prepared by MBAssociates un- 
der Bureau contract J0155084, Assessment of Optic Guid- 
ance, Control, and Supervisory Methods. The evaluation 
includes information on the employment of optical systems 
for the lateral alignment of a continuous miner. 

MBAssociates determined the characteristics of lateral 
alignment of a continuous mining machine, which affect 
the performance of optical guidance systems. They are 
listed as follows: 

1. Any optical path along the entry outby the continu- 
ous miner will be occluded from time to time. 

2. The percentage of occluded time increases as the 
seam height decreases. 

3. Face area illumination standards will strongly influ- 
ence the ambient light level. As a note, these standards 
would not be required in a fully automated face area. 

4. The continuous miner can be expected to make 
gross movements vertically and horizontally (several inches 
to a foot) while cutting. 

5. Any equipment mounted on top of the continuous 
miner is vulnerable to damage and contamination from 
roof falls, contact with the roof, and coal kicked back from 
the face. 

6. The continuous miner follows the coal seam, there- 
fore the entry will rise and fall along its length (line-of- 
sight is not reliable). 

Two basic lateral alignment systems using a vertical 
laser guidelines were investigated by MBAssociates. The 
first system is similar to the laser alignment sensor 



1 



developed by Bendix. The second system uses the same 
concept, but exchanges the position of the laser source and 
sensing unit. 

The first system, with the laser source mounted in the 
entry, was shown to have three disadvantages. First, a 
rehable system would require a large sensing imit. Other- 
wise, the laser guideline would be lost during the move- 
ments of the continuous mining machine during the cutting 
sequence, and the machine would shut down. Secondly, 
two laser guidelines would be required since two lifts are 
taken for each straight-cut. And, finally, the sepcu^ation of 
the sensing unit from the continuous miner would neces- 
sitate a data link to the continuous mining machine where 
none currently existed. 

The second system had the laser source mounted on the 
machine, and the sensing unit in the entry. The vertical 
laser guideline would be swept horizontally across the 
entry, analogous to a rastor scan, and the system would 
require only one laser guideline and one sensor. However, 
MBAssociates found disadvantages with the system in the 
extra complications with the horizontal sccuining hardware, 
and the separation of the sensing unit from the continuous 
miner. 

Another possible optical guidzmce system, investigated 
by MBAssociates, was a low-level pattern recognition sys- 
tem. Three narrow-band hght sources would be mounted 
on the continuous miner. A television camera would be 
positioned in the entry with its optical axis parallel to the 
centerUne of the desired cut. The position of the lights in 
the image would determine the lateral position and head- 
ing of the continuous miner. 

MBAssociates found two disadvantages with this system. 
The first disadvantage is the number of lights required for 
position and heading guidance. Three lights would be 
required to indicate the lateral displacement and heading 
of the continuous miner. The more Ughts used, the more 
chance that one will be blocked by an object. And again, 
a separation exists between the sensing unit and the con- 
tinuous miner. 

For all the optical systems considered, the major diffi- 
culty was maintaining the line-of-sight between the sensor 
and source. Shuttle cars proved to be the major obstruc- 
tion. The conclusion made by MBAssociates is that optical 
guidance system, such as those described, may not be sat- 
isfactory, especially with shuttle car haulage in the face 
area. 

Preliminary Design of Automated 

Continuous Mining Machine 

With Remote Override 

Ingersoll-Rand Resec^ch under Bureau contract 
H0242051, Preliminary Design of an Automated Continu- 
ous Mining Machine With Remote Override, contains the 
preliminary specifications for three automated continuous 
mining machines. Techniques are proposed for determin- 
ing heading displacement given an initial reference 
heading. 



The use of a gyroscope was suggested to provide 
heading displacement for the continuous miner. The de- 
sired heading of a cut would be initially given, and any 
small changes in heading could then be detected by the 
gyroscope. 

A gyroscope has an inherent drift in heading over time. 
Therefore, it requires realignment to some reference at 
regular intervals to maintiiin accurate readings. Ingersoll- 
Rand proposed that the gyroscope be realigned to true 
north at regular intervals by stopping the machine and per- 
forming a gyrocompassing procedure. They determined 
that the 10-min gyrocompassing procedure would be re- 
peated every 4 to 8 h. Since the specification of drift on 
the gyroscope to be used was 0.1°/h the drift error was 
tolerable. 

In today's market, however, a gyroscope with such a low 
drift costs $200,000. Reasonably priced gyroscopes, such 
as those used on miUtary vehicles today, have a much 
higher drift and would require the gyrocompassing proce- 
dure much too often. A gyroscope only provides a reading 
of change in heading, and provides no data on translational 
movements. It is not economically feasible to employ such 
a costly device when additional sensory systems are neces- 
sary to provide full guidance information. 

Ingersoll-Rand suggested the use of a magnetic flux- 
gate sensor to provide relative heading information. This 
electronic sensor directly measures the Earth's magnetic 
field to determine heading. However, owing to the mag- 
netic interference present on the continuous miner, the 
sensor's reading of absolute heading relative to true north 
is inaccurate, and cannot be used as a constant reference 
for entry heading. Nonetheless, Ingersoll-Rand suggested 
that a magnetic flux-gate sensor could possibly be used in 
a manner similar to the gyroscope and would provide reh- 
able measurements of small changes in heading, if the 
continuous miner were initially aligned to some known 
heading. 

CONCLUSIONS OF RESEARCH 

The previous discussions of the tasks of autonomous 
navigation in mines, and the research into sensors and 
navigational techniques (see appendix) leads to the follow- 
ing conclusions for the tasks of face, local, and global navi- 
gation of a continuous mining machine. 

Face Navigation 

Face navigation of a continuous mining machine con- 
sists of the task of controlling the position and heading of 
the continuous miner during the cutting process so that 
coal is removed according to the mine plan. This task re- 
quires that the continuous miner be provided with a refer- 
ence indicating the position and heading of the desired cut, 
along with precise guidance abilities. 



Reference for Desired Cut 



Guidance During Cutting Sequence 



Surveying marks, laser guidelines, or laser spots, the 
references currently used by continuous miner operators, 
cannot be relied upon as a continual indication of entry 
centerline unless they can advance and remain in close 
proximity to the working face and the continuous miner. 
In that case, a surveyor is required to place marks or 
advance the laser further into the entry as the machine 
advances. The surveyor's presence at the face would be 
frequently required owing to undulations in the seam, and 
the limitations in range of the guideline or the sensor to 
access the position of the surveyor's mark. This solution 
defeats the goal of removing workers from the working 
face. 

Compasses cannot be used as a constant reference for 
entry heading, owing to the magnetic interference caused 
by the large iron continuous mining machine. 

Laser-based guidance systems show promise to provide 
precise, reliable guidance for continuous mining machines 
when the Hne-of-sight is maintained. The major short- 
coming in previous laser guidance systems was the position 
of the laser or sensor in the entry. It was located in the 
center of the entry outby the continuous mining machine, 
causing a loss of line-of-sight by the shuttle car. If the 
laser or sensor was positioned on the sides or top of the 
entry and in close proximity to the continuous mining 
machine, this problem could most likely be eliminated. 

The sensory system employed to view the reference and 
determine the position of the continuous miner relative to 
the desired cut, should not fail if one sensor is not func- 
tioning properly. For example, the laser alignment sensor 
developed by Bendix used a single user guideline to indi- 
cate entry position and heading. The system is totally 
dependent on a single device. If the line-of-sight was not 
maintained, the operation of the machine would have to be 
suspended. To avoid this situation, relevant data should 
be gathered by multiple sensors and, if any sensors fail, 
other sensors will continue to provide adequate guidance 
information. 

In conclusion, the reference of the desired cut could be 
obtained by employing a multiple laser system mounted 
on a structure located near the face, and a sensor unit on 
the machine. The most reliable guidance would be ob- 
tained if the lasers were located on the sides or top of the 
entry, to best maintain the line-of-sight. The structure 
could initially be positioned at the face indicating the posi- 
tion and heading of the desired cut, providing the machine 
with the feedback information necessary for guidance at 
the face. When the machine completed a cutting cycle, it 
would stop, and the structure, if provided with some meth- 
od of self-locomotion, could advance in the entry using the 
stationary machine as a reference. 



Adequate guidance while advancing the face can be ob- 
tained by viewing the reference for the desired cut, and 
determining the relative position of the continuous miner 
with respect to that reference. 

In addition, the continuous miner must be able to navi- 
gate for a short period of time when it may not see the 
reference. Therefore, other sensory systems which do not 
require sight of the reference will be used to provide infor- 
mation when the referencing sensors fail or cue in error. 

Inertial reference sensors on the continuous miner 
could be used to maintain an accurate short-term knowl- 
edge of position and heading from a known initial location, 
thereby requiring the reference for the desired cut at reg- 
ular intervals rather than continually. At times when re- 
dundant, valid data are obtained from these multiple sen- 
sory systems, they will be combined to provide a greater 
and more reliable awareness of the position and heading 
of the continuous miner. 

Local Navigation 

Local navigation of a continuous mining machine con- 
sists of guidance and collision avoidance through entries 
and around corners. Adequate guidance and collision 
avoidance can be obtained by viewing the area in the 
direction of travel to find a clear path, and following the 
path while recognizing the presence and position of objects 
near the extremities of the machine to avoid collisions. 
The sensors and navigational techniques employed by vari- 
ous autonomous and remote vehicles in other local envi- 
ronments have been reviewed (see appendix), and many 
can be applied to the local navigation in the mine. 

Find Patli 

The machine must be able to see in the direction of 
travel to determine a path. Scanning range sensors, or 
sensors with a wide field-of-view are necessary to detest 
objects in the continuous miner's path. The range of the 
sensors must allow enough time for the continuous miner 
to take action to avoid an object in its path. 

The mounting of forward looking sensors on the contin- 
uous miner will be more difficult than on other mobile 
vehicles. A raised cutting head obscures frontal vision. 
Also, any sensors mounted toward the front of the contin- 
uous miner will experience maximum vibration and dust 
obscuration during the cutting cycle. Fragile imaging or 
scanning devices are not recommended since they will not 
survive this harsh treatment. 



Follow Path 



SUMMARY 



Ranging sensors, with their data processed with 
environmental modeUng techniques, provide a useful 
physical model of the immediate environment for local 
path following. To be specific, the position of ribs, 
crosscuts, or obstacles can be monitored with continually 
updated data from ranging sensors. The continuous miner 
is then provided with the information necessary for 
obstacle avoidance, wall following and guidance when 
traveling through entries and around corners in a mine. 

Reliable short-range collision avoidance of the large 
continuous mining machine in the close quarters of a mine 
is critical. As stated in the appendix, a reliable time-of- 
flight sensor with a wide field-of-view is the best ranging 
sensor for collision avoidance. Ultrasonic ranging sensors, 
commonly employed for obstacle avoidance on other 
autonomous vehicles, have a wide field-of-view, and show 
promise for reliability in the mine environment.^ 

Global Navigation 

Global navigation is the navigation among various 
points in the mine. The continuous miner requires a pre- 
programmed globed mine map along with the ability to 
generate and follow a path on the mine map. The map 
includes common travel routes, markers that may indicate 
global position, ventilation that may inhibit travel, or ter- 
rciin that cemnot be traversed. 

Generate Path 

The machine must be able to process the mine map and 
determine a path. Initially, the mining machine will be 
given its ciu-rent position relative to the mine map, and a 
final destination position. A few simple heuristics will 
provide the global path planning necessary in a mine (see 
appendix). 

Follow Path 

The continuous miner must be able to follow its chosen 
path. The current technology of inertial reference sensors 
does not provide long-term global positioning information. 
Markers could be made available at regular intervals; how- 
ever, these markers may get torn down by machinery or 
obscured by dust. The most promising method of global 
path following in a mine is simply to break the path down 
into a series of straight line segments, and count the cross- 
cuts passed and turns made to keep track of position rela- 
tive to the map. This information can be obtained from 
the environmental model developed for local navigation. 

^Bauzil, G., M. Droit, and P. Ribes. A Navigation Sub-System Using 
Ultrasonic Sensors for the Mobile Robot Hilare. Paper in Proceedings 
of First International Conference on Robot Vision and Sensory Con- 
trols, Stratford-upon-Avon, UK, Apr. 1-3, 1981, IFS, pp. 47-58. 

Oppenheim, I., and W. Whittaker. Demonstration of Robotic Map- 
ping of Mine Spaces. Eng. Constr. Rob. Lab., Carnegie-Mellon Univ., 
Pittsburgh, PA, Apr. 1985, 58 pp. 



The Bureau is proposing to develop a navigational guid- 
ance system to provide a continuous mining machine with 
the ability to navigate autonomously in a mine. Three 
types of navigation were identified: face, local, and global. 

Autonomous face navigation requires that the contin- 
uous miner be provided with an indication of the position 
and heading of the desired cut, and the abUity to monitor 
its movements at the face. A multiple laser-based guid- 
ance system mounted on a mobile reference structure is 
suggested. The system would provide the machine with 
the feedback information necessary to maneuver through 
the cutting sequences.. After a cutting sequence is com- 
plete, the structure could advance, using the stationary 
machine as a reference and maintaining an accurate indi- 
cation of entry position and heading. Inertial reference 
sensors could also be incorporated in this system to pro- 
vide short-term knowledge of the machine's position when 
the laser system may fail. 

Autonomous local navigation consists of the tasks of 
guidance and collision avoidance through entries and 
around corners. The machine must be provided with an 
ability to see in the direction of travel, and a knowledge of 
the position of the ribs and any obstacles. Ranging sen- 
sors, with their data processed with environmental model- 
ing techniques, provide a useful physical model of the 
immediate environment for local path following. Ultra- 
sonic ranging sensors, with their wide field-of-view, are 
suggested to obtain the data. 

Autonomous global navigation consists of the task of 
planning and following paths from one area in a mine to 
another. The machine must be provided with a prepro- 
grammed map of the mine, along with the ability to gen- 
erate and follow the planned path. The most promising 
method of global path following in a mine is simply to 
break the path down into a series of straight-line segments, 
and to count the crosscuts passed and turns made to keep 
track of position relative to the map. 

Of the three types of navigation in mines identified, the 
navigation of a continuous mining machine at the face is 
one of the more dangerous jobs in the mine. The high 
levels of noise and respirable dust, common at a working 
face, pose a personal health risk. Also, during the cutting 
process, the continuous miner operator is in close proxi- 
mity to unsupported roof. In the close confinement of the 
cab, the operator may lean out from the protective cover 
to gain a better view of the area. The operator is then ex- 
posed to the potential injury from falling rock. Also, the 
operator is endangered by possible explosions due to the 
higher concentrations of methane and dust, common at a 
working face. Consequently, many hazardous situations 
could be eliminated by automating the tasks performed by 
the continuous miner operator in the face area. Although 
automating these tasks alone will not eliminate the neces- 
sity for workers in mines, it will permit the immediate 
relocation of continuous miner operators from a highly 
dangerous environment to less hazardous areas, thus in- 
creasing the overall safety of the mine worker. 



10 



SENSORY SYSTEM, DATA MANIPULATION, AND CONTROL PROGRAMMING 



INTRODUCTION 

A decision to concentrate initial attempts on the tasks 
of autonomous face navigation has been made. This sec- 
tion outlines a proposed solution for autonomous face 
navigation of a continuous mining machine including the 
employment of a mobile roof support as a reference for 
guidance in the face area, a sensory system to provide 
navigation information, and algorithms for data manipu- 
lation and navigational control. 

AUTONOMOUS FACE NAVIGATION OF 
CONTINUOUS MINING MACHINE 



positions and headings necessary to execute a straight-cut 
and a crosscut in room-and-pillar type mining. The cutting 
sequences are as shown in figures 2 and 3. These cuts 
must also be executed according to the mine plan, to main- 
tain a safe amd productive mine. This task requires that 
the continuous miner be provided with a physical reference 
in the face area indicating the position and heading of the 
desired cut, and a navigational guidamce system consisting 
of a method to access the reference, to obtain a knowledge 
of its physical surroundings, and to control and monitor its 
maneuvers in the face area. 

Reference for Desired Cut 



The current goal of the project is to develop a naviga- 
tional guidance system to provide a continuous mining 
machine the ability to navigate autonomously through the 



The proposed solution is to employ a mobile control 
structure (MCS) as a reference for guidance in the face 
The MCS is currently under development at the 



area. 




6 



Figure 4.— Mobile roof support (MRS). 



11 



Bureau. It will provide a control center for all face oper- 
ations in a mine, and will conceivably serve many other 
functions, such as bolting the roof, providing a source of 
ventilation, performing methane checks, etc. However, 
when precisely positioned in the face area indicating both 
the position and heading of the desired cut, the MCS could 
provide a fixed, stable reference to guide all face navi- 
gation. The physical design of the MCS will be patterned 
after a mobile roof support (MRS), a commercially avail- 
able device designed to provide a temporary means of 
additional or alternative roof support (fig. 4). It consists 
of laterally spaced bars on four hydrauUcally powered 
wheels and four vertical hydraulic rams. The MRS is 
guided into position and the bars are forced against the 
roof by the rams. 



machine would refer to the position of the MCS as a refer- 
ence for alignment (fig. 5). During the cutting process, the 
continuous miner would continue to update its position 
and heading relative to the reference. The continuous 
miner would always be in close proximity to the MCS and 
could easily and frequently update its position and heading 
during both a straight-cut and crosscut sequence. 

After a full straight-cut is completed, the MCS would 
automatically advance 20 ft in the entry. It would use the 
position of the now stationary continuous mining machine 
as a reference, thereby maintaining a constant heading to 
guide the next cut. Also, it would have the abiUty to pivot 
90° and provide the reference for a crosscut. 

Benefits of Guidance From MCS 



Description of Guidance from MCS 

Initially, the MCS would be guided into place by a 
human using precise surveying equipment. As it is maneu- 
vered underneath the MCS, the continuous mining 



The MCS would provide a more protective environment 
for mounting of delicate sensors and equipment than the 
continuous miner. It would experience much less move- 
ment and vibration. The MCS and continuous mining ma- 
chine would function together via a communication link. 




Figure 5.— Continuous miner advancing the face under IVICS. 



12 



and gather and share environmental information. There- 
fore, the expensive and more fragile sensory systems (e.g., 
optical scanning devices) would be placed on the MCS, 
and the cheap passive targets and more rugged sensors 
would be placed on the continuous mining machine. 

The use of the MCS could eUminate more human inter- 
action in the face area. The MCS has the ability to func- 
tion not only as a reference for the continuous miner, but 
likewise as a reference for other mobile mining equipment, 
such as haulage vehicles and roof-bolting machines. At 
this time, their guidance is not the subject of research; 
however, if the MCS guidcuice techniques are successful 
for the continuous mining machine, then they could be 
easily applied to these other machines. Also, the MCS 
could provide a method of automatic ventilation, as re- 
quired by law, possibly by supporting and advancing a line 
curtain or by carrying an auxiliary fan or tubing. The need 
for human workers to be present at the working face 
would then be considerably reduced or eliminated. 

The use of the MCS could speed up the advancement 
of the face. It provides a means of roof support for an 
area past the last row of roof-bolts at the face. The 
continuous miner would then be safely able to advance the 
face further, thereby eliminating the number of place 
changes necessary to allow roof-bolting equipment access 
to the unsupported roof. 

Disadvantages of MCS Reference System 

The disadvantage in employing a MCS as a reference is 
that it is an additional mining vehicle to automate. The 
MCS would require its own autonomous positioning and 
guidance system, including sensors, processing capabilities, 
and motion control system. Obviously, the cost-benefit 
ratio is high when considering it only as a reference for the 
guidance of the continuous mining machine. However, in 
concept, the MCS would eventually be employed as the 
central guidance system for all vehicles in the face area. 
And, therefore, if one considers the resulting increase in 
production and decrease in labor force, the cost-benefit 
ratio would decrease. 

Navigational Guidance System 

Figure 6 is the proposed hardware-software systems and 
information transfer for a navigational guidance system 
providing autonomous face navigation for a continuous 
mining machine. 

Sensory Solution 

The previous section of this report indicated specific 
sensors, which show promise for the navigation of remote- 
controlled and autonomous mining vehicles. Laser-guided 
mining vehicles proved successful when the line-of-sight is 



maintained."* Also, another previous research attempt into 
the automation of continuous mining machines concluded 
that gyroscopes providing an inertial reference, with a 
periodic method to reference a known heading, could ef- 
fectively be used as a guidance sensor. Ultrasonic ranging 
systems have been demonstrated to be reUable for naviga- 
tion in mines,^ and for coUision avoidzmce on many mobile 
robots.* Also, the report indicated thai no one sensor 
should be reUed upon for guidamce information, but many 
sensors should be employed. Multiple sensors, with their 
data fused together, provide a more accurate and rehable 
aw£U"eness of the environment. 

As a result of the previous research, the following sen- 
sors have been selected. A gyroscope and a laser system 
has been chosen to be incorporated together for the pri- 
mary guidance information. A laser system mounted on 
the MCS will provide a direct reading of heading and posi- 
tion relative to the desired cut. A gyroscope mounted on 
the continuous miner will provide an inertial reference for 
heading, from the last heading determined from the laser 
system. An ultrasonic ranging system will be employed to 
obtain a knowledge of the physical surroundings. In addi- 
tion, a flux-gate heading sensor will be tested to determine 
its feasibility as a replacement or aid to the gyroscope. 
And, finally, inclinometers wUl be employed to provide a 
direct measurement of the pitch and roll of the continuous 
mining machine. 

The following is a description and implementation of 
the sensors that will be used to provide data for 
autonomous control of face navigation of a continuous 
mining machine. 

Laser-based Scanning System 

Lasernet,^ a laser-based optical scanning system devel- 
oped by Namco Controls, Mentor, OH, will be employed 
to access the reference and determine the position and 
heading of the machine relative to the desired cut. This 
relevant information will be gathered by multiple laser 
units, and if any units fail, others will continue to provide 
adequate guidance information. 

The Lasernet system contains a rotating mirror that 
sweeps a horizontal beam of laser light across a 90° field- 
of-view at a constant angular velocity. When the beam 
encounters a special 12-in tall cylindrical retroreflective 
target, the return beam is detected by a photodetector. 
This system can analyze information about the return 
beam and report the angle to the target. It is capable of 
determining the angular location of up to eight retroreflec- 
tive targets located within the planar and angular range of 
the scan. 



Work cited in footnote 2. 
^Second work cited in footnote 3. 
*First work cited in footnote 3. 

^Reference to specific products does not imply endorsement by the 
Bureau of Mines. 



13 



Sensor data 



(Engr. units) 



Monitoring 
systems 



Raw data 



from sensors 



Integration 
system 



Local 



model 



Navigational 

task 

scheduler 



Current Goal Local 
state, state, model 



Machine response (Ax,Ay,A^) 



Laser 

scanning 

system 



Gyroscope 

compass, 

inclinometers 



Ultrasonic 
ranging 
system 





Action controls 



to actuators 



Figure 6.— Block diagram of the hardware-software systems and information transfer for proposed navigational guidance system. 



Mtiltiple laser-scanning devices will be mounted on the 
MCS, and multiple targets wiU be mounted at a known 
separation on the continuous mining machine. A data link 
between the continuous miner and the MCS will provide 
the continuous miner with the feedback information neces- 
sary to determine its position and heading relative to the 
desired cut for aUgmnent and guidance at the face. 

Determining Position and Heading Using 
l-aser-Based Scanning System 

The position and heading of the continuous miner can 
be determined by two methods. 

Method 1: Given the angular position of two targets (A 
and B) of known position on the continuous miner relative 
to two laser-scanning devices (LI, L2) (fig. 7). 

The position of each target relative to LI (the desig- 
nated origin) can be determined using trigonometry. As 
shown in figure 8 for both targets A and B, the separation 
between the laser-scanning devices represents the length of 
the baseline, and each target position represents the vertex 
of a tricmgle. 



Since the separation between laser devices (dl2, dl2) 
is knovm, and the angles to the targets (6^^, 9^ and ^b„ 
9^2) are given, the length of the side (dAl, dBl) can be 
determined with triangulation. The position of each target 
relative to LI can then be determined by projecting the 
sides of the triangles onto the x and y dods. And, finally, 
the heading (h) of the targets relative to the centerhne of 
the cut (y axis) can be calculated from the two positions, 



h - tan" 



^B 



Ya - Yb 



Method 2: Given the angular position of three targets 
(D, E, and F) relative to one laser-scanning device (L3) 

(fig- 9). 

The position of the targets relative to L3 (the desig- 
nated origin) can be determined using trigonometry. As 
shown in figure 10, three triangles are formed by repre- 
senting the position of L3 as a common vertex, and the 
various target separations as the baselines of the triangles. 



14 





A(Xa,Ya) 




■>X 



I B(Xg,YQ) 



Figure 7.— Method 1 for determining position and heading of 
continuous miner relative to MCS. Angular position of two tar- 
gets (A,B) on the continuous miner relative to two laser scanning 
devices (L1,L2) is known. 



Fiqure 8.— Mathematcal representation of method 1 for posi- 
tion determination. 



Since these triangles share some common angles and 
sides, they provide three equations with three unknown 
values. These equations can be solved simultaneously, and 
the lengths of the sides (or sensor-to-target distances) can 
be determined. The position of each target relative to L3 
can then be determined by projecting these lengths onto 
the X and y axis. And, finally, the heading (h) of the tar- 
gets relative to the centerhne of the cut can be determined 
from two positions, as demonstrated in method 1. 

Both of these methods determine the position and 
heading of the targets on the continuous miner relative to 
the MCS. Each target's position on the continuous miner 
is known; therefore, the continuous miner's position and 
heading relative to the desired cut can be determined. 



15 




Figure 9.— Method 2 for determininq position and heading of 
continuous miner relative to MCS. Angular position of three 
targets (D,E,F) relative to one laser scanning device (L3) is 
known. 



Gyroscope 

A mechanical gyroscope will be used to maintain an 
accurate short-term knowledge of position and heading 
from the most recent laser referenced location. Mechan- 
ical gyroscopes have an inherent drift over time owing to 
small mass imbalances in the rotor, and require periodic 
recalibration to maintain accuracy. Therefore, the contin- 
uous miner must reference its heading with respect to the 




e^-eo 



Sf-Se 



Figure 10.— Mathematical representation of method 2 for posi- 
tion determination. 



desired cut from the laser-scanning system at regular 
intervals. 

When an accurate reading of heading is obtained from 
the laser-scanning system, the gyroscope will be calibrated. 
Any maneuvers involving turning desired by the continuous 
miner can then be controlled and monitored with the 
gyroscope. 

The incorporation of a gyroscope will increase the reli- 
ability of the laser referencing system by requiring the ref- 
erence for the desired cut at regular intervals, rather than 
continually. Therefore, the continuous miner will be able 
to navigate for a short period of time when it cannot see 
the reference or when the MCS referencing sensors fail or 
are in error. At times when redundant, vaUd data are 
obtained from these multiple sensory systems, it will be 
combined to provide a greater and more reliable aware- 
ness of the position and heading of the continuous miner. 

A directional gyroscope, Model #DG57-0602-l devel- 
oped by Humphrey, Inc., San Diego, CA, is to be em- 
ployed on the continuous miner. It experiences a mechan- 
ical drift of 0.1°/min. The desired accuracy in the heading 
of a cut is approximately 1.4° (6 in per 20 ft). Therefore, 
this gyroscope is usable as a heading indicator for 14 min 
without recalibration, more than enough time for execution 
of maneuvers requiring turning. 



16 



Ultrasonic Ranging System 

An ultrasonic sensor ranging system will be used to pro- 
vide a knowledge of the physical surroundings of the face 
area, i.e., the continuous miner's lateral position and head- 
ing relative to the ribs for alignment, and obstacle detector 
for forward and reverse tramming. In addition, the system 
will serve as another source of relative heading of the 
continuous miner. 

A system developed by Denning Mobile Robots, Inc., 
Woburn, MA, will be used. The system employs 24 
addressable time-of-flight ranging units consisting of 
environmental ultrasonic transducers developed for 
operation in severe environments. Each ranging unit is 
uniquely addressable and, upon request, returns a value 
corresponding to the range from the specified unit to the 
nearest object. 

The ultrasonic ranging units will be mounted on the 
continuous miner with their beams directed outward from 
the machine. Lateral position and heading information 
relative to the ribs will be determined from the units along 
the length of the machine. It is not necessary that the 
entire length of the continuous miner be covered in the 
field-of-view of the ranging units for lateral position and 
heading determination. However, the ranging units on the 
front and rear of the machine should cover the entire 
width of the continuous miner to provide reliable object 
detection for collision avoidance when tramming. 

Determining Lateral Position and Heading 
Using Ultrasonic Ranging Units 

The continuous miner will initially be assumed to be 
positioned at the face and outby the MCS. Therefore, it 
will rely on the ultrasonic ranging sensors to become posi- 
tioned parallel and at a safe distance from the ribs for for- 
ward tramming. 

The information necessary to align the continuous 
miner parallel to the ribs is the current angle of alignment 
and its lateral position in the entry. This method of align- 
ment is not as accurate as the laser-based scanning system, 
owing to the wide beam width, the diffuse surface of mine 
walls, and the potential presence of a line curtain. 

The angle of alignment of the continuous miner with 
respect to the ribs can be calculated from the measure- 
ments of two lateral sensors. The measurements from all 
the possible pairs of lateral sensors can be processed to 
determine the most accurate alignment angle. When 
monitored over time, they provide an indication of the 
relative heading of the continuous miner. 

Flux-Gate Heading Sensor 

A flux-gate heading sensor, developed by KVH Indus- 
tries, Middletown, RI, will be employed as a secondary 
measurement of instantaneous changes in heading. The 
absolute heading relative to true north will be unreliable 



owing to magnetic interference from the continuous min- 
ing machine. However, the sensor may provide accurate 
instantaneous changes in heading. 

A flux-gate heading sensor uses a solid-state electronic 
sensor, which directly measures the Earth's magnetic field. 
It is more reliable than a conventional magnetic compass, 
since it does not use magnets or rotating cards delicately 
balanced on jeweled bearings. It includes a micro- 
processor-based system which takes thousands of readings 
per second, interprets and averages them, and delivers the 
resultant heading information. 

The flux-gate heading sensor will be employed in the 
same manner as the directional gyroscope. Tests will be 
performed on the sensor to determine its precision and 
reliability on the continuous mining machine. 

Inclinometers 

Accustar Electric Clinometers, pendulum-type incli- 
nometers developed by Sperry Sensing Systems, Phoenix, 
AZ, will be employed on the continuous miner to provide 
the pitch-and-roU angle. These inclinometers employ a 
fluid and gas-filled capacitive sensor whose capacitance 
varies linearly with the rotation about its sensitive axis. 
This variation in capacitcmce is transformed into an elec- 
tronic signal and provides a direct measurement of tilt. 
Two inclinometers with their sensitive axis at right angles 
to each other will provide the pitch-and-roU angle of the 
continuous miner. 

Monitoring System 

Data Acquisition with BCC52 Computer-Controller 

The Micromint Basic-52 Computer-Controller (BCC52) 
will gather the data from the previously mentioned sensors. 
It is a stand-alone single board computer programmable in 
BASIC or machine language. Three BCC52's will be em- 
ployed, one dedicated to the laser-scanning system, one to 
the ultrasonic ranging system, and one to the gyroscope, 
compass, and inclinometers. 

The function of the BCC52's is to gather the raw data 
from their respective sensors, convert it into useful engi- 
neering units, perform low-level sensor integration if nec- 
essary, and deliver the data to a high-level computer. 

Low-Level Sensor Fusion of Multiple 
Laser-Based Scanning Systems 

Multiple laser-scanning systems provide a redundant 
source of information. Multiple values (V) of position and 
heading are calculated from the laser-scanning systems. 
By assigning weights (W) to the values and averaging this 
information, a more accurate and rehable value for posi- 
tion and heading of the continuous mining machine can be 
determined. 



17 



Each of the vcdues of position and heading [(V(1),V(2), 
V(3)...V(n)] will be assigned a confidence level [(C(l), 
C(2),C(3)...C(n)]. The confidence levels, representing the 
accuracy and reliability of the laiser system, can be deter- 
mined, in one way, from experiments of the system in a 
controlled environment. The experiments indicate items 
and conditions imder which the data are more accurate 
£md rehable. For example, the data from the laser scanner 
will most likely be more accurate when a greater angular 
separation exists between the targets in its field-of-view or 
when the target remains within a predetermined range. 
Other indications of confidence level are the last known 
position £md the current operating status of the machine. 
This information could indicate that the confidence of one 
laser scanner is low due to high dust concentrations, or 
that the laser is operating outside its accurate range. 

Average weights (W) for each value can be calculated 
from the percentage confidence levels. 

W(i) = C(i) / [C(l) + C(2) + ... + C(n)] 

The fused value, V(f), of position jmd heading is then 
determined by 

V(f) = W(l) * V(l) + W(2) * V(2) + ... + W(n) * V(n) 

These fused values for position and heading are deliv- 
ered upon request to the integration system. 

Integration System 

The integration system will request the data from the 
three monitoring systems, combine the position and head- 
ing values, and create an appropriate model of the face 
environment. 

Integrating Position and Heading Information 

The continuous miner's heading in the face area with 
respect to the desired cut (MCS) can be determined from 
the laser-scanning system, the gyroscope, and the ultra- 
sonic ranging system. First, the laser system's reading of 
heading, along with its associated confidence level, will be 
requested from the laser monitoring system. Secondly, 
the gyroscope's reading of heading change will be re- 
quested. This heading change along with the most recent 
referenced value of heading can be used to determine the 
current heading. The confidence level of this value can be 
obtained as a function of the length of time between read- 
ings. The fmal value of heading will be requested from the 
lateral sonar data. The associated confidence level can be 
determined from the inherent inaccuracies of the ultra- 
sonic rcinging units. 

The values of heading of the continuous miner with 
respect to the desired cut, along with their associated 
confidence levels, can be used to determine a fused value 



of heading and confidence. The method of averaging 
weighted values, as discussed earUer, will be employed. 

The value of lateral position of the continuous miner 
with respect to the desired cut can be determined in a sim- 
ilar manner, using the laser position data, and fusing it 
with the value of lateral position change relative to the ribs 
from the ultrasonic range data. The longitudinal position 
of the continuous miner with respect to the desired cut can 
only be determined by the laser system. Therefore, no 
data fusion, other than the low-level fusion of multiple 
laser units, is necessary for this information. 

Modeling the Face Area 

A geometric model indicating the continuous miner's 
position and heading relative to the actual physical bound- 
aries of the immediate area is essential for navigation. 
The graphical technique of modeling the environment 
developed by Turchan,* shows promise for the modeling 
of a mine environment. This technique requires range 
measurements from a designated center point on the vehi- 
cle to the closest objects at incremental angles of view. 
The data from the ultrasonic ranging system will provide 
the information. 

These range data, modeled as a function of angle, can 
be mathematically analyzed to provide a knowledge of the 
local environment. A large discontinuity in the function 
represents the edge of an obstacle, or perhaps the pres- 
ence of a crosscut. A discontinuity in the slope of the 
function represents a point where two walls meet, at the 
face or a corner. 

Navigational Goal Scheduler 

The navigational goal scheduler is a program, which will 
function as the scheduler of the progress of the continuous 
miner through the cutting sequence. It will contain two 
methods of scheduling, sequential and contingency. The 
schedulers observe and interpret the immediate world 
model and generate a desired position and heading, or 
goal state, of the continuous miner for the next sequence 
of tramming actions. 

The sequential goal scheduler has a predetermined list, 
in memory, of goal states for the execution of an ideal cut. 
If each of the goals is reached in the correct sequence, a 
cut will have been performed. 

The sequential scheduler analyzes the current position 
and heading of the continuous miner relative to the cur- 
rent goal state. If the goal was reached, the sequential 
scheduler recommends a next goal state to the action plan- 
ner. However, if the goal was not reached, control is 
transferred to the contingency goal scheduler. 

^Turchan, M. P., and A. K. C. Wong. Low-Level Learning for a 
Mobile Robot: Environmental Model Acquisition. Paper in Proceed- 
ings of IEEE Conference on Robotics and Automation, St. Louis, MO, 
Mar. 1985, pp. 156-161. 



18 



The contingency goal scheduler is necessary when, for 
one reason or another, the previous goal was not reached. 
The apparent problem is determined and an alternative 
goal state is recommended to the action planner. For 
example, when the continuous miner is slipping or stuck, 
the contingency goal scheduler will recognize the problem 
and may recommend a goal state in the reverse direction 
to try and free the machine. When the contingency goals 
have been reached, control will be restored to the sequen- 
tial goal scheduler. In addition, a history could be main- 
tained containing contingency goals and the success of the 
attempts at reaching these alternative goal states, to pro- 
vide the continuous miner with the ability to learn from 
its experiences. 

Action Planner 

The action planner is a program which plans, executes, 
and monitors a sequence of machine maneuvers to enable 
travel from the current position and heading to the goal 
state designated by the navigational goal scheduler. This 
program requires the knowledge of the primitive move- 
ments and the basic maneuvers of the continuous mining 
machine. 

The primitive movements describe the speed and direc- 
tion of tram for each track, and result in the basic maneu- 
vers of the continuous mining machine. Each track can be 
driven at two speeds, fast and slow, in both the forward or 
reverse direction. 

The basic maneuvers of the continuous miner are trans- 
lation, pivot, and turn. A translational movement is pos- 
sible in the forward or reverse direction, at fast or slow 
speed. A pivot is a rotation about the center axis of the 
continuous miner. It results when the two tracks are 
driven in opposite directions, and is only possible at slow 
speed. A turn is a rotation about one of the tracks, and 
results when one track is driven at slow speed, and the 
other track remains stationary. Because of the backlash in 
track drives and track slippage, none of these movements 
are performed with precision. 

The current state, goal state, and the environmental 
model are deUvered to the action planner from the 



navigational goad scheduler. A sequence of primitive 
movements is planned, by applying the rules of trigonom- 
etry along with the knowledge of the mobiUty of the con- 
tinuous miner. The sequence is executed by delivering the 
maneuvers sequentially to the machine control computer. 
The movement of the continuous miner is monitored 
through request of machine response information from the 
monitoring systems. 

A time limit will be set on the action plaimer's attempts 
to reach goal states. The action planner will continue to 
plan, execute, and monitor machine maneuvers until this 
time expires or the gocil state has been reached. If the 
goad state is reached, control will be returned to the 
sequential goal scheduler. However, if the time limit has 
expired, a navigational difficulty is occurring, such as 
the machine being stuck. In that case, control will be 
transferred to the contingency goal scheduler for a recom- 
mendation of an alternative goal state. 

Navigational Test-Beds 

Navigational experiments to evaluate sensor perform- 
ance and guidance algorithms will be conducted on two 
mobile test-beds. The Joy 16CM miner-bolter is the avail- 
able continuous mining machine for testing of navigational 
concepts (fig. 11). It is a drum-type continuous mining 
machine designed to extract coal in an underground mine 
using the technique of room-and-pillar mining. Another 
test-bed to be used for research into autonomous naviga- 
tion in mines is a locomotion emulator being developed 
for the Bureau by Carnegie Mellon University, Pittsburgh, 
PA. This test-bed will have the ability to emulate the loco- 
motion of many different mining vehicles currently in use, 
and is extendible to any future type of vehicles. 

Initial attempts at autonomous navigation will use the 
locomotion emulator as a full-scale model of a smaller 
continuous mining machine (e.g., Joy 12CM). The loco- 
motion emulator is a much more manageable mechanism 
to test the basic theories and concepts of navigation in 
mines. The Joy 16CM will initially be used to test the 
reHability of various navigational sensors on an actual 
mining machine. 



19 



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20 



CONCLUSIONS 



The Bureau is proposing to develop a navigational guid- 
ance system to provide a continuous mining machine with 
the ability to navigate autonomously through the positions 
and headings necessary to execute straight-cuts and cross- 
cuts in room-and-pillar type mining. These cuts must also 
be executed according to the mine plan in order to main- 
tain a safe and productive mine. This type of navigation 
has been classified as face navigation. Although two other 
types of navigation in mines are known to be needed, i.e., 
local and global, autonomous face navigation has been 
chosen as the short-term goal. Successful navigation at the 
face will result in a great increase in the overall safety of 
the mine worker, and many of the research issues of face 
navigation are applicable to the other types of navigation. 

Autonomous face navigation requires that the contin- 
uous miner be provided with an indication of the position 
and heading of the desired cut, a knowledge of its physical 
surroundings, and precise guidance abilities to control and 
monitor its movements at the face. 

A MCS will be employed as a reference for the desired 
cut in the face area. The MCS will be precisely positioned 
in the face area to provide a fixed, stable reference for 
both the position and heading of the desired cut. The 
continuous miner will refer to the MCS for alignment and 
guidance during the cutting process. 

A sensory configuration has been outlined for the navi- 
gational guidance of the continuous miner. Multiple sen- 
sor systems have been chosen to provide a more accurate 
and reliable awareness of the environment. Optical laser- 
based scanning devices will provide the continuous miner 
with the ability to reference the MCS. A mechanical 
directional gyroscope will be mounted on the continuous 



mining machine to provide relative heading information. 
A flux-gate heading sensor will be employed in a similar 
manner, and tests will be performed to determine its reli- 
abiUty with the magnetic interference present on the con- 
tinuous mining machine. Ultrasonic ranging units will be 
used to provide lateral position and heading information 
for alignment, and a front and rear obstacle detector for 
treunming of the continuous miner. Finally, two pendulum- 
type incUnometers will be employed on the continuous 
miner to provide the pitch-and-roU angle. 

Three monitoring systems consisting of the BCC52 
computer-controller will be used for acquisition of the 
sensory data. The BCC52's will gather the raw data from 
the sensors, convert it to useful engineering units, perform 
low-level sensor fusion if necessary, and deliver the data to 
the integration system. 

An integration system consisting of a BCC52 computer- 
controller will request the data from all the monitoring 
systems, integrate the position and heading of the contin- 
uous mining machine with respect to the desired cut, and 
create an appropriate model of the face environment. 

The navigational goal scheduler is a program which will 
schedule the progress of the continuous miner through the 
cutting sequence. This program will observe and interpret 
the model of the face area, and generate the next desired 
position and heading of the continuous miner. The current 
position and heading, and the next desired position and 
heading will be delivered to an action planning program. 
The action planner will generate, execute, and monitor a 
sequence of tramming actions to reach the next desired 
position and heading. 



21 



APPENDIX.-RESEARCH ISSUES IN AUTONOMOUS NAVIGATION 



An autonomous continuous mining machine requires 
methods of acquiring, processing, and manipulating 
navigational information to interact with objects in the 
mining environment. The methods used by autonomous 
vehicles in other environments are presented along with 
their apphcabUity for autonomous navigation of a 
continuous mining machine in a mining environment. 

METHODS OF ACQUIRING NAVIGATIONAL 
INFORMATION 

The fundcimental requirement for autonomous vehicle 
navigation in any environment is to acquire a represen- 
tation of the physical surroundings. This representation 
consists of the position of objects relative to the vehicle, 
and can be obtained from sensors providing range mea- 
surements from the vehicle to the object. 

Ranging Sensors 

The continuous miner ranging requirements can be clas- 
sified into two areas: positioning and collision avoidance. 
Positioning sensors require high accuracy and precision 
over a wide range, with a nairrow field-of-view. Collision 
avoidance sensors do not require the high accuracy, preci- 
sion, and range of positioning sensors. However, they do 
require a large field-of-view, and the outer range of the 
sensor should provide the continuous miner the time to 
stop when a collision is imminent. 

The following is a description of some of the methods 
of rcinging, which are employed for both positioning and 
collision avoidance on existing autonomous vehicles. The 
various techniques for ranging are discussed, followed by 
the sensing mediums employing these technologies, with 
attention focused on their functionaHty on a continuous 
mining machine in the mine. 

Techniques for Ranging 

Time-of-Flight 

The time-of-flight ranging technique provides range to 
an object by measuring the time it takes for a pulse of 
energy to travel from a transmitter to the object and back 
to a receiver. The range can then be calculated by multi- 
plying the velocity of the pulse by one-half of the time 
required to travel the distance. 

The time-of-flight sensors maintain reliability as long as 
the return signal is received and detected. The reception 
and detection of the return signal is dependent on the dis- 
tance to the object, the strength of the transmitted signal, 
and the characteristics of the reflecting surface. As the 
range to the object increases, the intensity of the return 



signal decreases. Obviously, a transmitted signal of greater 
strength provides a return signal at greater ranges. How- 
ever, a maximum range exists where a return signal can no 
longer be detected by the receiver. No signal would be 
received when the tremsmitted signal is reflected from a 
smooth object whose surface is at an angle from the trans- 
mitter. However, these specular reflections will not 
present many difficulties in a mine environment, where 
the diffuse surface of the mine walls are most often the 
reflecting object for range measurements. It is likely, 
however, that the transmitted signal will scatter after en- 
countering the rough surface, and those signals could re- 
flect from secondary objects and provide a false return 
signal to the receiver. 

The appUcations of time-of-flight ranging systems are 
related to the beam width of the signal being transmitted. 
The distance determined by time-of-flight ranging systems 
is the distance to the closest point which the signal encoun- 
ters. If the transmitted signal has a wide beam width, the 
exact angular position of the object relative to the sensor 
is not known. Wide beam, time-of-flight ranging systems 
cannot be used for precise object positioning, but are very 
appropriate for collision avoidance. 

Triangulation 

The triangulation technique of ranging requires two 
sensors at a known separation on the vehicle providing the 
angle to the same object. It utilizes the basic trigonom- 
etric property of triangles. That is, when given the length 
of one side (separation between the sensors) and two an- 
gles of a triangle (angles from the sensors to the object), 
the lengths of the two remaining sides (ranges from the 
sensors to the object) of the triangle can be calculated. 

The range accuracy of a system employing the tech- 
nique of triangulation is dependent on the accuracy of the 
measured angles and, furthermore, the variations in angu- 
lar position to an object decrease as a function of distance. 

One type of triangulation ranging, similar to human 
vision, uses two camera images. The range to the object 
is inversely proportional to the displacement of the object 
on the image planes. The ranging becomes more accurate 
the further apart the imaging devices are, or the closer the 
object is. However, if the imaging devices are too far 
apart or the object is too close, the object may not appear 
in both images. 

The major difficulty of this type of ranging system is 
that the same object has to be identified accurately in both 
images. These systems typically use the ambient light to 
illuminate the object. In a mining environment, however, 
an artificial source of light must be provided, and not 
many objects are present in a mine which are easy to 
identify. 



22 



Another method of triangulation ranging is demon- 
strated in the commercially available Lasernet system, 
which can measure and report the angular location of 
special cylindrical retro-reflective targets. The system 
consists of a scanning laser source and a photodetector. 
When the laser hits the retro-reflective target, a reflected 
beam is returned and detected by the photodetector. Since 
the laser is scanned at a constant angular velocity, the time 
between the steu^t of the laser's sweep and the moment at 
which the reflected beam returns from the target can be 
used to calculate angular position. The angular positions 
of the target relative to two Lasernet units and the sepa- 
ration between these units, can be used to determine the 
range to the target. 

In summary, triangulation ranging systems are limited 
in range accuracy by their ability to measure small angles 
precisely. The long-range accuracy can be improved by 
increasing the separation between the two sensors. 

Interferometry 

Interferometry offers extremely precise and accurate 
distance measurements. Interferometry is based on the 
interference patterns that result between two energy waves 
that travel paths of different lengths. If the length of the 
path for one of the energy waves is increased, the two 
waves interact and produce constructive and destructive 
interference. By observing this interference pattern and 
knowing the wavelength of the source, it is possible to 
calculate the relative distance the two energy waves have 
traveled at fractional wavelength accuracies. This distance 
can be the change in position of a target on a moving 
vehicle relative to some previous position. 

A retro-reflector target is required on the vehicle in 
order to provide a reliable return signal for the interfer- 
ometer. The distance measured by interferometry ranging 
is the change in distance along the straight-line path from 
the transmitter to the target. The angles of this straight- 
line path must be known to determine the displacement of 
the target in each coordinate direction. 

The disadvantage of interferometry ranging is that it 
provides only relative distance measurement. Therefore, 
the usable measurements are cumulative and require a 
constant line-of-sight between the target and system. 
Interferometry would not be reliable in a mining environ- 
ment owing to the frequent occurrence of loss of the line- 
of-sight caused by other machinery, dust, or rocks. 

Sensing Mediums for Ranging . 

Acoustic Signals 

Acoustic ranging can be accomplished by using the 
previously discussed techniques of time-of-flight and tri- 
angulation. Ultrasonic energy (acoustic energy of fre- 
quencies above the limits of human hearing) is commonly 
used for ranging devices on mobile vehicles. 



The wide beam width of ultrasonic waves introduces 
some uncertainty in the perceived distance to and the 
anguleir position of an object. The range obtained is the 
distance to the first object in the field-of-view of the sen- 
sor, and may not be the distance to the object in the beam 
centerline. Therefore, it functions best as a collision 
avoidance sensor, by detecting the presence of the nearest 
object in a wide field-of-view. 

An ultrasonic wave may not be reflected back to the 
receiver if it encounters a specular surface at an angle. 
Therefore, ultrasonic ranging devices function much more 
reliably in an environment with diffuse surfaces, such as in 
a mine. These surfaces scatter the transmission and most 
often reflect a signal back to the receiver. The use of 
acoustic sensors for navigation in mines was demonstrated 
with Carnegie Mellon University's Terregator vehicle.^ 
The vehicle was tested at the Bureau experimental mine, 
and successfully navigated in the mine environment using 
ultrasonic ranging sensors. 

Optical Ranging 

Optical ranging can be accomplished by using the pre- 
viously discussed techniques of time-of-flight, triangulation, 
and interferometry. Imaging systems employing vision are 
commonly used for guidance or road following, and optical 
laser-based ranging systems are commonly used for precise 
positioning of autonomous vehicles. 

Any type of ranging system employing vision imaging 
devices are not presently being considered for use in the 
mine. There is no natural source of ambient light, thus 
artificial illumination would have to be provided. Also, the 
amount of data manipulation necessary is too great to jus- 
tify vision over simple ranging devices. 

Optical ranging devices employing laser sources provide 
a quick and accurate method of ranging. They have a very 
narrow beam width and are most appropriate for the pre- 
cise positioning information required during the execution 
of the cutting sequence at the face. 

Radar 

Radar uses the time-of-flight technique to determine 
the range to an object. Radar employs radio frequency 
energy. It has an advantage over optical and acoustical 
waves in that it can propagate through dust. 

Radar systems employing electromagnetic waves are 
best suited to very long ranges. The high velocity of elec- 
tromagnetic waves induces the possibility of transmitter- 
receiver interference at shorter ranges. Therefore, expen- 
sive and complicated circuitry is necessary to produce a 
signal that is short in duration. 

'Oppenheim, I., and W. Whittaker. Demonstration of Robotic Map- 
ping of Mine Spaces. Eng. Const. Rob. Lab., Camegie-Mellon Univ., 
Pittsburgh, PA, Apr. 1985, 58 pp. 



23 



Microwave energy waves are also used in radar systems. 
Ranging devices employing these waves can be configured 
to function over ranges suitable to mobile vehicle re- 
quirements, and provide collision avoidance by detecting 
the presence (not precise position) of an object. They are 
best suited as presence detectors, such as level indicators 
or back-up alcu^ms for manned vehicles. However, they 
provide Uttle resolution for autonomous vehicle 
apphcations. 

METHODS OF PROCESSING NAVIGATIONAL 
INFORMATION 

Mapping Techniques 

The continuous miner requires a geometric model of 
the local environment. One possible method of environ- 
mental modeling of the local area in a mine is the graph 
synthesis approach, developed by M. P. Turchan.^ This 
approach requires range measurements to the closest 
objects around the vehicle at incremental angles of view. 

A center point on the machine is chosen as an origin 
point for the range measurements. The model is obtained 
by examining the value of range from the origin to the 
nearest object as a function of the angle-of-view of the 
sensor (0 to 360°). 

Applications of Graph Synthesis Model 
to Mine Model 

The range data from the continuous miner's sensors 
modeled as a function of angle can aid in path planning 
and entry navigation. The discontinuities of the function 
itself represent the edge of an obstacle, or perhaps the 

^urchan, M. P., and A. K. C. Wong. Low-Level Learning for a 
Mobile Robot: Environmental Model Acquisition. Paper in Proceed- 
ings of IEEE Conference on Robotics and Automation, St. Louis, MO, 
Mar. 1985, pp. 156-16L 



presence of a crosscut. The discontinuities of the slope of 
the function represent the points where two walls meet, 
possibly at the face or at a corner. These representations 
of the environment can be an aid to both local and global 
navigation. 

INTELLIGENT TECHNIQUES FOR 
NAVIGATIONAL CONTROL 

A method of global path planning is necessary for the 
continuous mining machine. This planning requires a map 
programmed in memory indicating the paths of travel in a 
mine. 

Global Path Planning 

The continuous miner must be able to determine a safe 
and traversable path to a destination given a reliable map 
of the area between the current position and destination. 
Many popular techniques exist for finding the optimal path 
and are used by other autonomous vehicles. 

Many techniques of path planning for other mobile ro- 
bots involve depicting the maps in a graph form with costs 
assigned to possible routes. In the case of mine travel, 
those costs may represent distance, risk, maneuverability, 
or traversabillty. A search Is performed on the graph, and 
the lowest cost path is chosen. 

However, global path planning in a mine does not re- 
quire complex programming algorithms. Most mines have 
designated main passageways for travel in a particular 
direction. Since most of the travel is done along these 
routes, the only planning necessary is for the short travel 
from the main passageways to the work area. The plan- 
ning techniques are uncomplicated due to the regular and 
parallel nature of paths in a mine. This planning involves 
choosing a path from among many similar parallel entries 
and crosscuts. Any safe path with a minimal number of 
turns can be chosen. A few simple heuristics can provide 
the global path planning necessary in a mine. 



U.S. GOVERNMENT PRINTING OFFICE: 611-012/00,053 



INT.BU.OF MINES,PGH.,PA. 28881 



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